Talk:A20 line

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This is a really a note to myself but if anyone else wants to tackle before I get around to it then they can.

This article really additional information. Such as the segemented memory model of the x86 architecture and how this translates to the address lines of the chip. Also the 8042 chip should be mentioned in relation to its role with the A20 line. Mention AT and XT arcitectures. -- Popsracer 10:29, 31 Jul 2003 (UTC)

I'm extremely dubious of the expansion of the A in A20 as "above". I'm fairly certain that the name simply derives from the fact that the hardware implementation gated this signal from the keyboard controller (8042) with the address line A20 from the microprocessor. --Brouhaha 21:36, 14 Oct 2004 (UTC)

I removed the following information as it is misleading/incorrect.

"Letter "A" in the name A20 refers to "Above", while "20" refers to the 20th power of 2. (2²⁰ bytes = 1 Mbyte)"

A20 refers to Address line 21. In real mode there are 20 address lines A0-A19. With a 286, 386, etc, there are more than 20 address lines, ergo, the 21st address line is A20 and must be pulled low to enable to address wrapping mentioned in the article. Sure the power of 2 information is correct only coencidently in that every time you add an address line, you raise the addressable region by a power of two. In the context it was presented, it is misleading. I can't imagine a simple, relevant way to describe these things, I think its better to just let them be deleted.

A20m should be disabled VMX instructions [From Wanchun Wang]